I will try it again Chris, but it is the second attempt with it as I now have a suitable 3/8 magmount ,the last test was on a friend's mag but I'm getting same on mine.
Don't get me wrong it's ok but I know if it were longer I'd get even lower.

Sounds like by what you say that some previous has cut the threaded end to SWR instead of the other end of it. Find a length of steel or brass wire the same dia and thread it to the length you require with an appropriate thread die.

Sounds like by what you say that some previous has cut the threaded end to SWR instead of the other end of it. Find a length of steel or brass wire the same dia and thread it to the length you require with an appropriate thread die.

As it screws onto the aerial itself rather than the magnetic base/ground-plane, surely it shouldn't noticably affect the radiation pattern?
I was thinking if it physically added an inch onto the height of the aerial, it might mean the top-screw could then be adjusted more.